Thermal Analysis of Cretaceous Ambers from Southern France
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Thermal analysis of Cretaceous ambers from southern France Eugenio RAGAZZI University of Padua, Department of Pharmacology and Anaesthesiology, largo E. Meneghetti 2, I-35131 Padova (Italy) [email protected] Aurelio GIARETTA Institute of Geosciences and Earth Resources (IGG-CNR), corso Garibaldi 37, I-35137 Padova (Italy) Vincent PERRICHOT Paleontological Institute, University of Kansas, Lindley Hall, 1475 Jayhawk blvd, Lawrence, KS 66045 (USA) [email protected] Didier NÉRAUDEAU Université Rennes I, UMR CNRS 6118 Géosciences, campus de Beaulieu bât. 15, 263 avenue du Général Leclerc, F-35042 Rennes cedex (France) [email protected] Alexander R. SCHMIDT Georg-August-Universität Göttingen, Courant Research Centre Geobiology, Goldschmidtstr. 3, D-37077 Göttingen (Germany) and Museum für Naturkunde der Humboldt-Universität zu Berlin, Invalidenstr. 43, D-10115 Berlin (Germany) [email protected] Guido ROGHI Institute of Geosciences and Earth Resources (IGG-CNR), via Matteotti 30, I-35137 Padova (Italy) [email protected] Ragazzi E., Giaretta A., Perrichot V., Néraudeau D., Schmidt A. R. & Roghi G. 2009. — Thermal analysis of Cretaceous ambers from southern France. Geodiversitas 31 (1) : 163-175. ABSTRACT Th ermal properties of French Cretaceous ambers were investigated and compared with other ambers from various sites of the world. Th e amber samples came GEODIVERSITAS • 2009 • 31 (1) © Publications Scientifi ques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com 163 Ragazzi E. et al. from 10 diff erent localities in southern France, in the Charentes, Languedoc, and Provence regions, ranging from Late Albian to Santonian in age. Th ermo- gravimetric (TG) and Diff erential Th ermogravimetric (DTG) profi les were obtained at heating rate of 10 K/min in air, starting from room temperature (20°C) and reaching a maximum temperature of 700°C. Elemental Analysis for total Carbon, Hydrogen, Nitrogen and Sulphur was also carried out. Th e TG combustion profi le of the resins started after 200°C and complete combustion took place near 600°C. Th e DTG behaviour is characterized by a main exo- thermal peak situated between 394 and 420°C, accompanied by minor peaks and shoulders. Th e increasing value of the main exothermal peak correlates well to the increase of the age of the specimens, with a signifi cant correlation coeffi cient (r = 0.7721, p = 0.0089). A signifi cant correlation (r = 0.6728, p = 0.0004) is also found with other samples of diff erent age and origin. By con- sidering the whole pattern of DTG peaks, a possible fi ngerprinting model of the French ambers is evaluated by multivariate analysis. Cluster Analysis and Principal Component Analysis show the presence of several clusters, according to the geological age and possibly to the palaeobotanical origin. Th e elemental analysis is consistent with that of other Cretaceous samples from diff erent sites of the world. Carbon and hydrogen are the main constituents (range 73-80% and 9.5-11.5% respectively). Sulphur is detected in small amounts (0.8-2.4%). KEY WORDS Nitrogen is absent or appears as traces only (0-0.008%). Oxygen and other ele- Th ermal analysis, ments range from 4.6 to 16.8%. No successful clustering was possible according elemental analysis, to the elemental composition. Th ermal analysis, completed with multivariate amber, Cretaceous, statistics, is a useful source of information also for French ambers, as a help for France. identifi cation of the age, diagenetic processes and palaeobotanical origin. RÉSUMÉ Analyse thermique des ambres crétacés du Sud de la France. Les propriétés thermiques des ambres crétacés de France sont évaluées et comparées avec celles d’autres ambres de sites variés. Les échantillons d’ambre proviennent de 10 localités diff érentes du Sud de la France, dans la région des Charentes, en Languedoc, et en Provence, et ont un âge compris entre l’Albien terminal et le Santonien. Les profi ls thermo-gravimétriques (TG) et thermo-gravimétriques diff érentiels (DTG) ont été obtenus à un taux de réchauff ement de 10 K/min dans l’air, débutant à température ambiante (20°C) et atteignant une tempéra- ture maximale de 700°C. L’analyse élémentaire du total de carbone, hydrogène, azote et soufre a également été eff ectuée. Le profi l TG des résines débute après 200°C et la combustion complète se situe autour de 600°C. Le comportement DTG est caractérisé par un pic exothermique principal situé entre 394 et 420°C, ainsi que par des pics et variations mineurs. Les valeurs croissantes du principal pic exothermique et de l’âge des échantillons d’ambre montrent un coeffi cient de corrélation signifi catif (r = 0,7721, p = 0,0089). Une bonne corrélation (r = 0,6728, p = 0,0004) est aussi observée avec d’autres ambres d’origine et d’âge distincts. Une analyse statistique multivariée considérant l’ensemble des pics DTG permet d’établir un profi l caractéristique des ambres français. Une analyse de clusters et une analyse en composantes principales montrent plu- sieurs regroupements en accord avec l’âge géologique et possible ment l’origine paléo botanique des résines. La composition élémentaire est cohérente avec celle d’autres ambres crétacés. Carbone (73-80 %) et hydrogène (9,5-11,5 %) sont les principaux constituants, alors que le soufre est présent en petite quantité (0,8-2,4 %) et que l’azote est absent ou présent seulement à l’état de traces 164 GEODIVERSITAS • 2009 • 31 (1) Th ermal analysis of Cretaceous French amber (0-0,008 %). L’oxygène et les éléments traces varient entre 4,6 et 16,8 %. La MOTS CLÉS composition élémentaire ne permet pas d’établir de regroupements signifi catifs Analyse thermique, des diff érents ambres analysés. L’analyse thermique, complétée par des analyses analyse élémentaire, statistiques multivariées, s’avère donc informative tant du point de vue de l’âge ambre, Crétacé, que de celui des processus diagénétiques et de l’origine paléobotanique, et per- France. met d’affi ner la caractérisation des ambres de France. INTRODUCTION from diff erent geographical sources (Broughton 1974; Rodgers & Currie 1999; Ragazzi et al. Amber is a fossil organic polymer which origi- 2003; Feist et al. 2007). It is a rapid quantitative nates from tree resins through complex matura- method which aims to examine the overall pyrolysis tion processes collectively named “amberization” process and then to estimate the eff ective rates of (Anderson & Winans 1991; Anderson et al. 1992; overall decomposition reactions. Th e fi rst studies Anderson & Crelling 1995). Th is process includes (Broughton 1974; Rodgers & Currie 1999) have oxidation, oligomerization and cross-linking, which demonstrated the ability of thermal analysis to take place in the resin soon after its secretion by detect specifi c characteristics of various kinds of the plant. Several diff erent parameters can play recent and fossil resins, with the oldest samples relevant roles in amber composition, for example from the Eocene (about 40-45 Ma) and the Late the original environment (as a complex mixing of Cretaceous (about 70 Ma). Further investiga- temperature, light irradiation, climate and possible tions conducted in our laboratory extended the pathogen intervention, which infl uence the resin application of the thermal analysis to more an- composition), the palaeobotanical origin, the dia- cient fossil resins, till the Upper Triassic (about genetic history, the geological age, and also possible 225 Ma; Ragazzi et al. 2003). Under diff erential alterations which occurred after amber mining. thermogravimetric (DTG) analysis, all samples Th e characterization of amber can be achieved presented a main exothermal event, whose tem- using several methods of analysis, such as Fourier perature varied among resins, showing signifi cant transformed infra-red analysis (FTIR), pyrolysis-gas linear correlation, on the basis of the geological chromatography-mass spectrometry and nuclear age (Ragazzi et al. 2003). magnetic resonance (Broughton 1974; Lambert & Th e availability of recently discovered Albian Frye 1982; Beck 1986; Grimalt et al. 1988; An- to Santonian (about 100 to 85 Ma) amber from derson & Winans 1991; Anderson et al. 1992; France (Néraudeau et al. 2002, 2003, 2008, 2009 Anderson & Crelling 1995; Carlsen et al. 1997; this volume; Gomez et al. 2003; Perrichot 2005; Martínez-Richa et al. 2000). Th e chemical analysis Perrichot et al. 2007a, b), suggested an investiga- of the basic components of the polymer may fail tion of the thermal properties of these peculiar to reveal diff erences among fossil resins since the fossil resins, and a comparison with the behaviour specimens, although of the same geological age of other ambers from various sites of the world. and similar composition, may display diff erent In particular, the mid-Cretaceous ambers from maturity grades, for example as a consequence of Charentes region, whose deposits are the largest higher temperatures and chemical linkages which in France, were considered. Besides thermogravi- occurred during fossilization. metric investigation, an elemental analysis was Th ermogravimetric analysis has been introduced also carried out on the same samples in order as a new method to provide additional informa- to further defi ne the amber physico-chemical tion on the physico-chemical properties of amber characteristics. GEODIVERSITAS • 2009 • 31 (1) 165 Ragazzi E. et al. TABLE 1. — Characteristics of the French amber samples investigated. Abbreviations in brackets are those used elsewhere in this paper.